The field of this invention relates to an improved method for producing viscous oils utilizing steam stimulation.
Many sources of heavy oils are available in various parts of the world. One of the largest is the Athabasca tar sand region in Alberta, Canada. Somewhat similar oils exist in California. To the present time, production of these wells has been difficult for various reasons.
Frequently, the sandstone reservoirs in which heavy oils occur contain at least partially unconsolidated sands or friable sands. Production of sand leads to serious consequences with the production equipment.
To avoid sand production, it has been customary to use a gravel pack. Such gravel packs are conventionally used where unconsolidated sands are present.
To produce the heavy oils discussed above, which may have a viscosity in the range of a few hundred to several million centipoise, it has been suggested that one use steam stimulation. By the nature of the deposit, such steam injection rates often reach and exceed the formation parting pressure. This in turn precludes the use of a gravel pack for controlling sand production as the gravel would be washed into the fracture upon steam stimulation.
An object of this invention is to provide an improved process for the production of heavy oils.
A further object of this invention relates to a process for producing viscous oils with a combination of steps including stimulating the well by injecting steam at a pressure sufficient to fracture the reservoir, shutting in the well, inserting a conventional gravel pack, producing oil, and periodically stimulating the well by injecting steam at a pressure below that which would result in a well fracture.
Other objects and advantages of this invention will be apparent to one skilled in the art upon reading this disclosure.